Method and apparatus for measuring acceleration or mechanical forces

ABSTRACT

A method for measuring acceleration or mechanical forces, the acceleration causing inertial forces, uses a transducer or accelerometer in which at least one piezoelectric element is influenced by a shearing force substantially parallel to the polarization axis of the piezoelectric element, where the shearing force is created by a component of a mechanical or an inertial force substantially perpendicular to the polarization axis. A transducer for measuring acceleration or mechanical forces, the acceleration causing inertial forces, includes at least one piezoelectric element and at least two spaces surfaces abutting the piezoelectric element and arranged so that they are mutually displaced by a component of a mechanical or an inertial force acting substantially in a direction perpendicular to the polarization axis of the piezoelectric element. The piezoelectric element is preferably mounted between the free ends of two arms positioned on a supporting base, the arms being deformed or tilted in a direction perpendicular to their longitudinal axis by the force or acceleration. Forces or accelerations in three directions may be measured using a single piezoelectric element with a plurality of electrodes. The principles are also useful for the measurement of force or pressure.

FIELD OF THE INVENTION

This invention relates to transducers employing piezoelectric elementsfor generating an electrical output in accordance with mechanicalinfluences to which the piezoelectric element is subjected. Theinvention finds particular application in accelerometer transducers forgiving electrical outputs in accordance with acceleration.

BACKGROUND OF THE INVENTION

Mechanical dynamometers are often used for static and dynamicmeasurements of mechanical forces. The forces to be measured may causechanges in the electrical charge, voltage, current or impedance in oneor more measuring elements.

When measuring mechanical vibrations or acceleration it is known to useseismic accelerometers employing piezoelectric material for generatingthe electrical charges. For such accelerometers it is known to have aseismic mass arranged on the piezoelectric element or material whichagain is arranged on a base. Thus, when the accelerometer is subjectedto acceleration, inertial forces introduce strains in the ceramicelement which produces electrical outputs by virtue of the piezoelectriceffect.

When vibrations having a frequency which is substantially lower than thenatural resonant frequency of the total accelerometer system are actingupon the base, the seismic mass is forced to follow the vibrationsthereby acting on the piezoelectric element with a force which isproportional to the seismic mass and the acceleration. Thereby, theinertial force acting on the piezoelectric element generates electricalcharges on the element which charges are proportional to theacceleration.

When the piezoelectric element is subjected to compression forces duringvibration, the accelerometer is of the compression type, and when thepiezoelectric element is subjected to shear forces during vibration, theaccelerometer is of the shear type. The compression type accelerometeris the most simple in its construction, but it is rather sensitive totemperature transients since the ceramic piezoelectric material ispyroelectric in the axis of polarization and the signals is taken fromelectrodes perpendicular to this axis. In contrast to this, the sheartype accelerometer has a low sensitivity to temperature transients asthe signal here is taken from electrodes parallel to the axis ofpolarisation.

It is known that a higher sensitivity can be obtained by anaccelerometer of the "bender" type. In such an accelerometer, the forcefrom the seismic mass acts to bend a so-called "bender element", whichhas a layer of an electric conductive material sandwiched between twolayers of piezoelectric material being polarized in their direction ofthickness. Thus, when the element is bent, then, in a planeperpendicular to the longitudinal axis of the element, stresses ofcompression are generated in one of the two layers and stresses oftension are generated in the remaining layer. When the length of thebender element is considerable larger than the thickness of the element,the electrical charges generated on each of the two layers will belarger than the charges obtained if the same seismic mass is operatingdirectly for the purpose of compression or shear of the piezoelectricmaterial.

However, a disadvantage of the bender element is that it ispyroelectric, since the electrodes are arranged on surfaces which areperpendicular to the axis of polarization.

Another disadvantage of the bender element is that the piezoelectricmaterial constitutes a major part of the mechanical construction whichcauses some problems when trying to optimize this construction.

SUMMARY OF THE INVENTION

It is therefore a principal object of this invention to provide a methodand a transducer in which the pyroelectric effects of the piezoelectricmaterial are reduced or avoided. According to the principles of thepresent invention this is done by using the shear sensitivity of thepiezoelectric material while at the same time having the force of theseismic mass amplified.

The principle of the present invention is illustrated in FIG. 1. In FIG.1 two arms 1, 2 are shown both of which are secured in one end to arelatively stiff base 3 by two hinges 4, 5 and in the other end aresecured to oppositely positioned surfaces of a piezoelectric element 6which element is polarized in the longitudinal direction of the arms 1,2.

When the system of FIG. 1 is influenced by a force P perpendicular tothe longitudinal axis of the arms 1, 2 at a distance L from the axis ofthe hinges, a moment M=P×L is generated at the securing points. Thehinges 4, 5 are only able to transfer shear or compression forces; thus,the moment M will not be transferred by the hinges, but the result willbe a force couple P_(f1), P_(f2) with the arm h, where P_(f1), P_(f2)and the distance h fulfil the equation:

    P×L=P.sub.f1 ×h=P.sub.f2 ×h

or

    P.sub.f1 =P.sub.f2 =P×L/h.

Thus, the force P perpendicular to the longitudinal axis of the arms istransformed to a force couple P_(f1), P_(f2) acting in the longitudinaldirection of the arms. The forces P_(f1), P_(f2) are L/h times the forceP and impose a mechanical stress on the piezoelectric element.

From the above discussion it should be understood that according to theprinciples of the present invention, it is possible, by arranging aseismic mass with its centre of gravity at a distance L from the axis ofthe hinges, to produce an accelerometer having a sensitivity which isL/h times larger than for an accelerometer where the same seismic massis arranged to act directly on the piezoelectric element or elements,while at the same time obtaining the low dynamic temperature sensitivitywhich is characteristic for accelerometers of the shear type.

It is therefore a principal object of the invention to provide animproved method for measuring acceleration or mechanical forces, wherethe acceleration causes inertial forces, using a transducer or anaccelerometer in which at least one piezoelectric element is influencedby a shearing force substantially parallel to the polarization axis ofthe piezoelectric element. In accordance with the principles of theinvention this shearing force is created by a component of a mechanicalor an inertial force being substantially perpendicular to thepolarization axis of the piezoelectric element.

When a shearing force or forces acts or act on a piezoelectric element,electrical charges are created on surfaces of the element whereby anelectrical voltage may be generated across said piezoelectric element.The charges or voltage may be used in order to determine the componentof the mechanical force or the component of the acceleration resultingin the shearing force.

Preferably the shearing force is created by a mutual displacement of atleast two spaced surfaces, with the displacement having a componentsubstantially parallel to the axis of polarization of the piezoelectricelement and being caused by the mechanical or inertial force. For themechanical or inertial force component to create the shearing force itis preferred that the piezoelectric element or elements is or aremounted in an intermediate and abutting relationship with the surfaces.

It is preferred that the piezoelectric element or elements is or aremounted between and in shear relationship with a first and a second oftwo substantially oppositely positioned surfaces, and in a preferredembodiment, a first piezoelectric element and a second piezoelectricelement are mounted between and in shear relationship with said firstand second substantially oppositely positioned surfaces, respectively.However, more than two piezoelectric elements may be arranged betweenthese surfaces. In order to obtain a good sensitivity to the forcesacting on the piezoelectric elements, the polarization axes of thepiezoelectric elements should be substantially parallel to each other.However, the polarisation axes may be opposed to each other.

In order for the two spaced surfaces to be mutually displaced by themechanical or inertial force component and thereby creating the shearingforce, it is preferred that each of the said two oppositely positionedsurfaces are part of one of two arms or uprights positioned on asupporting base. The arms should be fastened to the base so that thearms are deformed or tilted in relation to the supporting base by saidforce component.

The form of the piezoelectric element or elements may vary, however, inorder to maximize the sensitivity of the transducer, it is preferredthat the piezoelectric element or elements has or have substantiallyparallel surfaces extending in the direction of the axis ofpolarization. Hence, when the piezoelectric element or elements is orare being influenced by said generated shearing force, electricalcharges are generated on the surfaces of the piezoelectric element orelements. Thus, the generated charges or a corresponding generatedvoltage difference may represent a measure of the force componentcreating the shearing force. The substantially opposite parallelsurfaces of the piezoelectric element or elements may be plane surfacesor cylindrical surfaces.

It should be understood that according to the principles of theinvention it is possible to measure force components having differentdirections by having different directions of the surfaces of thepiezoelectric element or elements.

Thus, in a preferred embodiment, a measure of a first mechanical orinertial force component substantially perpendicular to the polarizationaxis is obtained from first charges being developed on a first pair ofparallel surfaces of the piezoelectric element or elements, and ameasure of a second mechanical or inertial force component, which issubstantially perpendicular to the polarization axis and substantiallyperpendicular to the direction of the first force component, is obtainedfrom second charges being developed on a second pair of parallelsurfaces of the piezoelectric element or elements.

Furthermore, a tri-axial measurement may be performed by furthermeasuring a third mechanical or inertial force component substantiallyparallel to the polarization axis of the piezoelectric element orelements, with a shearing force being created by said third forcecomponent. It should be understood that a measurement in two directionsmay also be performed by combining the measurements of the first and thethird force components.

Another object of the invention is to provide a transducer or anaccelerometer which is able to measure a mechanical force or anacceleration according to the principles of the present invention. Thus,according to the invention, a transducer or an accelerometer is providedcomprising at least one piezoelectric element and at least two spacedsurfaces abutting said piezoelectric element. These surfaces arearranged so that they are mutually displaced when a component of amechanical or an inertial force acts substantially in a directionperpendicular to the polarization axis of the piezoelectric element.

In order to obtain mechanical stress within the piezoelectric element orelements and thereby creating a shearing force, it is preferred that thepiezoelectric element or elements of the transducer are positionedbetween and in shearing relationship with the two spaced surfaces. It isfurthermore preferred that the two spaced surfaces are arranged so thatthey are substantially opposed to each other.

Thus, when the spaced surfaces are mutually displaced by the forcecomponent, the piezoelectric element or elements will be influenced by ashearing force substantially parallel to the polarization axis of thepiezoelectric element or elements, thereby generating an electricalsignal which may be output from the piezoelectric element or elementsand used for determining the mechanical force component or theacceleration component.

It is preferred that the transducer has two ore more piezoelectricelements mounted between and in shear relationship with said twosubstantially oppositely positioned surfaces, where the piezoelectricelements have substantially parallel polarization axis. Furthermore itis preferred that the two spaced surfaces of the transducer are part ofone or two arms or uprights positioned on a supporting base, the armsbeing deformed or tilted in relation to the supporting base when theforce component is acting on at least one of the arms.

In order to obtain an electrical output signal when measuring amechanical force or an acceleration, it is preferred that the transducerfurther comprises first electrical output means for outputting a firstelectrical output signal being developed across a first pair ofsubstantially parallel surfaces of the piezoelectric element orelements, said first output signal representing a measure of a firstmechanical or inertial force component substantially perpendicular tothe polarization axis.

It is furthermore preferred that the transducer comprises secondelectrical output means for outputting a second electrical output signalbeing developed across a second pair of substantially parallel surfacesof the piezoelectric element or elements, said second output signalrepresenting a measure of a second mechanical or inertial forcecomponent, which is substantially perpendicular to the polarization axisand substantially perpendicular to the direction of the first forcecomponent.

In order to obtain a tri-axial transducer it is also preferred that thetransducer comprises third electrical output means for outputting athird electrical output signal being developed by a shearing forceacting on the piezoelectric element or elements, said shearing forcebeing generated by a third mechanical or inertial force componentsubstantially parallel to the polarization axis of the piezoelectricelement or elements.

It should be understood that the transducer or accelerometer accordingto the present invention may be constructed to incorporate any of thefeatures presented in this specification and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments and details of the system appear from the claims and thedetailed discussion of embodiments of the system given in connectionwith the accompanying drawings in which:

FIG. 1 is a schematic illustration of the principles of the invention,

FIGS. 2 and 3 show embodiments of a symmetrical transducer according tothe invention,

FIG. 4 shows an embodiment of a transducer with two piezoelectricelements in accordance with the invention,

FIG. 5 shows an embodiment of a transducer with four piezoelectricelements in accordance with the invention,

FIG. 6 shows an embodiment of a transducer in accordance with theinvention in which the piezoelectric element is formed as a block with acylindrical hole,

FIG. 7 shows an embodiment of a transducer in accordance with theinvention having an annular piezoelectric element, and

FIG. 8 shows a presently preferred embodiment of a transducer inaccordance with the invention having an annular piezoelectric element.

DETAILED DESCRIPTION OF THE INVENTION

In the example shown in FIG. 1, the arms 1, 2 are secured to the base 3by use of hinges 4, 5 allowing the arms to be tilted in relation to thesupporting base.

However, it should be understood that it is not necessary to secure thearms by use of hinges, but it is preferred that the attachment of thearms to the base is performed in such a way that deformation or tiltingof the arms in relation to the base by a force perpendicular to thelongitudinal axis of the arms is facilitated. Thus, it is preferred thateach of the arms themselves is substantially more easily tilted inrelation to the supporting base than the combination of the two arms andthe piezoelectric element or elements.

This is illustrated by the embodiments shown in FIGS. 2 and 3. FIG. 2shows a symmetrical transducer having two pair of arms 21a, 21b and 21c,21d secured to a base 22 where the tilting of the arms is facilitated bynotches 25a, 25b and 25c, 25d. Between each pair of arms 21a, 21b and21c, 21d, a piezoelectric element 23 and 24, respectively, issandwiched, and a pair of seismic masses 26a, 26b and 26c, 26d isarranged on the outer surface of the arms 21a, 21b and 21c, 21d,respectively. The axes of polarization of the piezoelectric elements 23and 24 are indicated by the arrows 27 and 28, respectively. In thisembodiment of the invention, the construction of the transducer issymmetrical in order to obtain balance of the system and thereby reduceor avoid transverse movements in the transducer construction.

If the electrical signals from the two piezoelectric elements 23 and 24are added, the transducer will mainly be sensitive to forces oraccelerations in a direction given by the arrows 29 and 30, and if thesignals from the two elements are subtracted, the transducer will mainlybe sensitive to angular forces or angular accelerations around an axisperpendicular to the plane given by the arrows 27, 28, 29 and 30.

FIG. 3 shows another symmetrical transducer similar to the transducer ofFIG. 2, but with the seismic masses 36, 37 sandwiched betweencorresponding pairs of piezoelectric elements 33a, 33b and 33c, 33d,respectively. The reference numerals of FIG. 3 are otherwise similar tothe reference numerals of FIG. 2. If the seismic mass 36 equals the sumof the seismic masses 26a and 26b, the arm lengths from the notches 25aand 25b to the centre of gravity of the corresponding seismic mass ormasses 36 or 26a and 26b are equal, and if the distances between thehinges which may be represented by the notches 25a and 25b in FIGS. 2and 3 are equal, the shearing force acting on the piezoelectric element23 in FIG. 2 will equal the shearing force acting on the piezoelectricelements 33a and 33b in FIG. 3.

FIG. 4 shows a transducer corresponding to one half of the transducershown in FIG. 3, but turned 90° so that the axis of polarization of thepiezoelectric elements is in the direction of the z-axis of the systemof co-ordinates. In FIG. 4 the two arms are referred to by 41a and 41b,the two piezoelectric elements are referred to by 42 and 43 withsurfaces 42a, 42b and 43a, 43b, respectively, the two notches arereferred to by 44a and 44b, the seismic mass is referred to by 45, andthe base is referred to by 46.

It is preferred that the surfaces 42b and 43a are in conductingengagement with the seismic mass 45 which should be made from aconductive material with the result that the potential of surface 42bequals the potential of surface 43a. When measuring an acceleration inthe z-direction in accordance with prior art technique the twopiezoelectric elements act in parallel with the substantial samepotential difference being generated from surface 42a to surface 42b andfrom surface 43b to surface 43a. This voltage can be obtained bygrounding the surfaces 42a and 43b and by measuring the voltage of theseismic mass 45.

However, accelerations in the x-direction may be measured according tothe principles of the present invention by having the two piezoelectricelements 42 and 43 in series. Having the same potential for the surfaces42b and 43a, the surface 42a may be grounded and the electrical seriesoutput may be output from the surface 43b. It should be noted that theelectrical output signal may represent the electrical charges generatedat the surface 43b.

Thus, with the arrangement of a transducer as shown in FIG. 4 it ispossible to bring output signals to a combined summation and differenceamplifier and thereby measure acceleration in two directions which areperpendicular to each other.

If the direction of polarization of the piezoelectric element 43 isturned substantially 180°, the output signals from the elements 42 and43 should preferably be combined in parallel when measuringaccelerations in the x-direction and in series when measuringaccelerations in the z-direction.

If it is desired to measure accelerations or forces in all three axes ofthe system of co-ordinates, this can be accomplished by having a secondpair of piezoelectric elements arranged on the seismic mass 45. This isillustrated in FIG. 5 which shows a tri-axial accelerometer where theprinciples of the present invention is used when measuring in thex-direction and the y-direction, whereas the acceleration in thez-direction is measured in accordance with prior art techniques.

The transducer of FIG. 5 comprises piezoelectric elements 51, 52, 53 and54 which are all polarized in the z-direction of the transducer oraccelerometer. All four elements 51, 52, 53 and 54 have their innersurfaces in conducting engagement with a seismic mass 55, which ispreferably made of a conducting material, whereas their outer surfacesare abutting four corresponding arms 58a, 58b and 59a, 59b. The elementsmay be clamped between the arms and the seismic mass by a clamping ringsurrounding the arms. The arms are arranged on a base 57, and it ispreferred that the arms have notches 60a, 60b and 61a, 61b (61a and 61bare not shown) in order to facilitate tilting when measuringaccelerations or forces in the x-direction or the y-direction.

It is preferred that the outer surface of element 51 is connected toground, and that the two elements 51 and 52 are connected in series inorder to feed a signal to an x-output for measuring accelerations orforces in the x-direction. Correspondingly, it is preferred that theouter surface of element 53 is connected to ground, and that the twoelements 53 and 54 are connected in series in order to feed a signal toan y-output for measuring accelerations or forces in the y-direction.Both the x-signal and the y-signal may be connected to charge amplifiersdelivering the x-output and the y-output, respectively.

When the transducer in FIG. 5 is vibrated in the z-direction, thesignals of all four elements 51-54 are summed at the seismic mass 55,since the input at the charge amplifiers of the x-output and they-output are virtually zero. Thus, when measuring forces oraccelerations in the z-direction, the signals from all four elements51-54 are used in parallel and an output signal for measurements in thez-direction is taken from the seismic mass 55 and fed to a voltageamplifier in order to obtain a z-output.

When vibrating the transducer in the x-direction or the y-direction thecorresponding pair of elements are connected in series. Each element insuch a pair of series connected elements has the substantially samecapacity and the same resulting charges, and if the first element insuch a pair is connected to ground and the second element is connectedto virtually zero at the charge amplifier, the centre of such a pairwill also have a voltage of zero. Thus, no or only a small error signalwill be generated in the non-vibrating directions, even if all theelements 51-54 are electrically connected to each other at the centrepoint, which may be represented by the seismic mass 55.

It is important to notice that the output signal feeding the z-output isnot capacitively loaded, since a vibration in the z-direction otherwisecould result in a current being drawn from the centre point to ground.Thus, the voltage amplifier at the z-output should preferably be anamplifier with a low input capacity.

FIG. 6 shows a tri-axial transducer or accelerometer measuring along thesame principles discussed in connection with FIG. 5. However, in FIG. 6the four elements 51-54 of FIG. 5 are replaced by one piezoelectricelement formed mainly as a block 62 having a substantially cylindricalhole 63. The outer surfaces 64-67 of the block 62 correspond to theouter surfaces of the elements 51-54 in FIG. 5. The reference numeralsin FIG. 6 are otherwise similar to the reference numerals of FIG. 5.

There is no separate seismic mass in the transducer of FIG. 6, since theweight of the block 62 will operate as a seismic mass when measuring inthe z-direction. Furthermore, when measuring in the x-direction and they-direction the masses of the arms and the clamping ring will alsocontribute to the total seismic mass. However, a separate seismic massmay be introduced into the hole 63 in order to obtain a greatersensitivity of the transducer.

Another example of a tri-axial transducer or accelerometer is shown inFIG. 7. This transducer corresponds to the transducer of FIG. 6,however, the piezoelectric block 62 is now replaced with a piezoelectricelement 72 having a substantially annular cross section with a hole 73.The surfaces 74, 75, 76 and 77 abutting the arms 58a, 58b and 59a, 59bwhich are formed to engage with these surfaces, correspond to thesurfaces 64-67 in FIG. 6. It should be understood that the transducer ofFIG. 7 will operate in a way corresponding to the transducer of FIG. 6,but the annular construction may be produced at lower costs.

FIG. 8 shows a presently preferred embodiment of a tri-axial transduceror accelerometer operating according to the principles discussed inconnection with FIG. 5. A piezoelectric ring 72 is polarized in theaxial direction, and a cylindrical seismic mass 55 made of tungsten issoldered into the piezoelectric ring 72. Four arms 58a, 58b, 59a, and59b (59a and 59b are not shown) are positioned adjacent to thepiezoelectric ring 72, and an insulating ring 81 insulates the four arms58a, 58b, 59a, and 59b from a clamping ring 82 of steel pressing thefour arms firmly against the piezoelectric ring 72. Each of the fourarms 58a, 58b, 59a, and 59b is supported by a corresponding hinge 60a,60b, 61a, and 61b (61a and 61b are not shown) that electrically andmechanically interconnects the corresponding arm to a thickfilm circuitboard 84 containing three amplifiers. The thickfilm circuit board 84 isglued into a base 57, which is made of titanium and comprises anintegrated electrical connector. A wire 86 connects the cylindricalseismic mass 55 to the amplifier for the z-direction. The housing 87 ofthe transducer is made of titanium, and is externally shaped as a cube.The housing 87 has a cylindrical bore, into which the base 57 is pressedand welded to the housing.

The accelerometer shown in FIG. 8 has the following specifications:

    ______________________________________                                        Sensitivity before amplifier (X and Y directions):                                                    9            pC/g                                     Sensitivity before amplifier (Z direction):                                                           10           mV/g                                     Resonance frequency (X and Y directions):                                                             8            kHz                                      Resonance frequency (Z direction):                                                                    10           kHz                                      Weight:                 15           gram                                     ______________________________________                                    

Although only a limited number of embodiments of the invention has beenspecifically disclosed and described herein, it will be obvious that theinvention is not limited thereto, but is capable of being embodied inother forms as well. Furthermore, the invention is not limited to themeasurements of acceleration, but may for example be employed ininstruments that measure force or pressure.

I claim:
 1. A transducer for measuring acceleration or mechanical forceswith said acceleration causing inertial forces, said transducercomprising:at least one piezoelectric element having a polarizationaxis, a supporting base, two arms or uprights placed on the supportingbase, the two arms or uprights being deformable or tiltable in relationto the supporting base by a component of a mechanical or an inertialforce acting substantially in a direction perpendicular to thepolarization axis of said at least one piezoelectric element, and atleast two spaced surfaces, the at least one piezoelectric element beingmounted in between the at least two spaced surfaces, each of said atleast two spaced surfaces being part of one of the two arms or uprights,and the at least two spaced surfaces being arranged so that they aremutually displaceable by said force component to create a shearing forcein the at least one piezoelectric element in a direction substantiallyparallel with its polarization axis, wherein, each arm or upright of thetwo arms or uprights comprises a region of relatively reduced thicknessacting as a hinge means and being located adjacent to the supportingbase.
 2. A transducer according to claim 1, wherein the at least twospaced surfaces are arranged so that they are substantially opposed toeach other.
 3. A transducer according to claim 2, wherein two or morepiezoelectric elements of the at least one piezoelectric element aremounted in between substantially opposed surfaces of said at least twospaced surfaces, said two or more piezoelectric elements havingsubstantially parallel polarization axes.
 4. A transducer according toclaim 1, wherein the at least one piezoelectric element hassubstantially parallel surfaces extending in the direction of the axisof polarization of the at least one piezoelectric element, and whereinelectrical charges are developed on said substantially parallelsurfaces, when the shearing force is created in the at least onepiezoelectric element by displacement of said two arms or uprights saidcharges representing a measure of said force component creating theshearing force by mutually displacing said at least two spaced surfaces.5. A transducer according to claim 4, wherein the substantially parallelsurfaces of the at least one piezoelectric element are opposite planesurfaces.
 6. A transducer according to claim 5, wherein thesubstantially parallel surfaces of the at least one piezoelectricelement are opposite cylindrical surfaces.
 7. A transducer according toclaim 6, further comprisinga first pair of substantially parallelsurfaces of the at least one piezoelectric element, and first electricaloutput means for outputting a first electrical output signal beingdeveloped across said first pair of substantially parallel surfaces ofthe at least one piezoelectric element; said first output signalrepresenting a measure of a first mechanical or inertial force componentsubstantially perpendicular to the polarization axis of the at least onepiezoelectric element.
 8. A transducer according to claim 7, furthercomprisinga second pair of substantially parallel surfaces of the atleast one piezoelectric element, and second electrical output means foroutputting a second electrical output signal being developed across saidsecond pair of substantially parallel surfaces of the at least onepiezoelectric element, said second output signal representing a measureof a second mechanical or inertial force component, which issubstantially perpendicular to the polarization axis and substantiallyperpendicular to the direction of the first force component.
 9. Atransducer according to claim 8, further comprisingthird electricaloutput means for outputting a third electrical output signal beingdeveloped by a shearing force acting on the at least one piezoelectricelement, said shearing force being generated by a third mechanical orinertial force component substantially parallel to the polarization axisof the at least one piezoelectric element.
 10. A transducer according toclaim 1, wherein each of the two arms or uprights themselves are moreeasily tilted in relation to the supporting base than the combination ofthe two arms or uprights and the at least one piezoelectric element. 11.A method for measuring acceleration or mechanical forces, saidacceleration causing inertial forces,said method comprising:providing atransducer comprising: at least one piezoelectric element having apolarization axis; a supporting base; two arms or uprights placed on thesupporting base, the two arms or uprights being deformable or tiltablein relation to the supporting base by a component of a mechanical or aninertial force acting substantially in a direction perpendicular to thepolarization axis of the at least one piezoelectric element; each arm orupright of the two arms or uprights comprising a region of relativelyreduced thickness acting as a hinge means and being located adjacent tothe supporting base; and at least two spaced surfaces, the at least onepiezoelectric element being mounted in between the at least two spacedsurfaces, each of the at least two spaced surfaces being part of one ofthe two arms or uprights, and the at least two spaced surfaces beingarranged so that they are mutually displaceable by the force component;providing inertial forces or mechanical forces, said inertial forcesbeing caused by acceleration, said forces having a first component beingsubstantially perpendicular to the polarization axis of the at least onepiezoelectric element; deforming or tilting the two arms or uprights inrelation to the supporting base so as to mutually displace the at leasttwo spaced surfaces and so as to create, in the at least onepiezoelectric element, a shearing force substantially parallel to itspolarization axis; and outputting a first electrical signal across afirst pair of substantially parallel surfaces of the at least onepiezoelectric element, said first output signal representing a measureof said first mechanical or inertial force component.
 12. A methodaccording to claim 11, wherein a first piezoelectric element and asecond piezoelectric element of the at least one piezoelectric elementare mounted in between a first and a second of two substantiallyoppositely positioned and spaced surfaces, respectively, of the at leasttwo spaced surfaces, said first and second piezoelectric elements havingsubstantially parallel polarization axes.
 13. A method according toclaim 11, wherein two or more piezoelectric elements of the at least onepiezoelectric element are mounted in between a first and a second of twosubstantially oppositely positioned and spaced surfaces of the at leasttwo spaced surfaces, said two or more piezoelectric elements havingsubstantially parallel polarization axes.
 14. A method according toclaim 11, wherein the at least two spaced surfaces are parallel andextend in the direction of the axis of the polarization, and wherein thedeforming or tilting step comprises developing electrical charges on theat least two spaced surfaces, said charges representing a measure of theforce component creating the shearing force.
 15. A method according toclaim 14, wherein the first pair of substantially parallel surfaces ofthe at least one piezoelectric element are plane surfaces.
 16. A methodaccording to claim 14, wherein the first pair of substantially parallelsurfaces of the at least one piezoelectric element are cylindricalsurfaces.
 17. A method according to claim 14, wherein the providedmechanical or inertial force has a second mechanical or inertial forcecomponent, which is substantially perpendicular to the polarization axisof the at least one piezoelectric element and substantiallyperpendicular to the direction of the first force component, the methodcomprising the step of obtaining a measure of said second mechanical orinertial force component from second charges developed on a second pairof parallel surfaces of the at least one piezoelectric element.
 18. Amethod according to claim 17, further comprising measuring a thirdmechanical or inertial force component substantially parallel to thepolarization axis of the piezoelectric element or elements, with ashearing force being created by said third force component.